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Freshwater Salinization Syndrome Alters Nitrogen Transport in Urban Watersheds
Citation:
Galella, J., S. Kaushal, P. Mayer, C. Maas, R. Shatkay, S. Inamdar, AND K. Belt. Freshwater Salinization Syndrome Alters Nitrogen Transport in Urban Watersheds. WATER. MDPI, Basel, Switzerland, 15(22):3956, (2023). https://doi.org/10.3390/w15223956
Impact/Purpose:
Our study addresses the phenomenon of freshwater salinization syndrome (FSS) where salts, especially NaCl from road salts, can exacerbate the mobilization of heavy metals and ions into combinations of chemical pollutants that we term “chemical cocktails”. We described how FSS can mobilize nutrients including nitrate and nitrites with potential to pollute streams in the Chesapeake Bay watershed and exacerbate eutrophication of the Chesapeake Bay estuary. This study leveraged multiple datasets to show that freshwater salinization may significantly impact nitrogen transport and by altering timing of nitrogen delivery and amplifying peaks of nitrogen transport to downstream waters especially in urban ecosystems.
Description:
Anthropogenic salt inputs have increasingly impacted many streams in the U.S. for more than a century. Urban stream salinity is often chronically elevated and punctuated by episodic salinization events after applications of road salt, which can last hours to days after snowstorms. Here, we investigated the impacts of freshwater salinization on total dissolved nitrogen (TDN) and NO3- / NO2- concentrations and fluxes across time in five urban watersheds in the Baltimore-Washington D.C. Metropolitan area of the Chesapeake Bay region. Concentrations of TDN, NO3- / NO2- and specific conductance (SC) were monitored in all five sampled urban streams, which were USGS monitoring stations. In addition, continuous NO3- / NO2- data was obtained from sensor measurements at a nearby USGS site in Virginia for comparisons with the other 5 sampled sites. Targeted snowstorm sampling was conducted at Sligo Creek from 2019 to 2021. Results show that episodic road salt events quickly mobilized total dissolved nitrogen in the nontidal streams monitored. Each of the urban streams had elevated levels of TDN, NO3- / NO2- and SC concentrations, which rapidly peaked during and after winter road salt events, and then declined. Hourly mass fluxes of TDN also followed this same peak pattern. Plateaus in TDN concentrations at the highest SC values (between 1,000 and 2,000 μS/cm) during road salt events were recorded. Plateaus in nitrogen (N) concentration suggested an eventual source limitation of TDN after ion exchange in soils (and other geochemical and biological processes). When comparing our study watersheds to a forest reference watershed, there was a positive relationship between Cl- loads and NO3- / NO2- loads across all sites regardless of land use, which suggests that mass transport of Cl- and NO3- / NO2- can be influenced by similar factors (likely build and flush of Cl- and NO3- / NO2- in soils and hydrologic mechanisms). However, our results also suggest that there can be concentration thresholds in the transport of N in watersheds influenced by road salt events. Freshwater Salinization Syndrome (FSS) may interact with build and flush dynamics in some urban watersheds and amplify peaks in N transport to alter the timing of N delivery to sensitive receiving waters during winter months.
